My first programming job and the first time I had access to a lan of decent computers, introduced me to Quake deathmatch. A friend and collegue of mine, Nick Maher implemented Quake world local a LAN version of ID Software's quake world server software. It logged frags and deaths and ranked the players in the office in the same way the Internet quake world server did. We were very serious about our Quake for a long time, Nick often kicked our butts but eventually we improved and had some awesome competion going. We would have beers and watch demos of Thresh in the Red Annihlation finals and comment on his playing style like we would any other sport. That is what deathmatch first person games are for me, a sport, fast reflexes, accuracy, skill, tactics and strategy all make or break a deathmatch player. It proves, for me, that a simple concept for a game can create complex behaviour in players.
VGA Planets is a turn based, play by email, space empire building game. Up to 11 races (which seem strangly familiar to factions in various popular science fiction films and TV shows) battle for galactic supremcy over months and possibly years of real time playing. Each week, my friends and I would process our respective turns, give orders to ships, manage resources and send abusive subspace messages to each other. The turns would be submitted by all players and processed by the host. This simple system worked very well and created the kind of political and military machinations that I have not seen in any other game. Alliances were made and broken, fleets changed sides mid conflict and many galactic warlords were stabbed in the back by their trusted allies.
I played System Shock about 2 years after it came out, you would think that the game would have dated a little, it hadn't. This is the first computer game I played that had such an incredible atmostphere that it gave me nightmares. This game totally avoided the problems of stilted NPC characters by killing everyone before the player arrives. Despite the untimely death of all the Citadel station employees, character development is created with the logs of the dead npc's scattered around the station.